1. Field of the Invention
2. Description of the Prior Art
A conventional hex wrench 1 in accordance with the prior art shown in FIG. 2 comprises a handle 11 and a head 12 connected with the handle 11. The handle 11 has a distal end provided with a first mounting portion 111. The head 12 has a distal end provided with a second mounting portion 121. In operation, the first mounting portion 111 of the handle 11 or the second mounting portion 121 of the head 12 is inserted into the hexagonal hole of a hex hole screw to rotate the hex hole screw so as to tighten or loosen the hex hole screw. At this time, the handle 11 or the head 12 is subjected to a torsional shear stress that is applied by the hex hole screw during operation of the hex wrench 1. However, the hex wrench 1 is usually made of a medium steel which has a smaller stiffness or hardness to reduce the torsional radius of the hex wrench 1 so that the hex wrench 1 is easily distorted or deformed due to an excessive applying force. Alternatively, the hex wrench 1 can be worked by a heat treatment to increase its stiffness or hardness. However, the malleability of the hex wrench 1 is decreased after the heat treatment to reduce the torque of the hex wrench 1 so that the hex wrench 1 is easily cracked or broken due to an excessive torque.
The present invention is, therefore, arisen to obviate or at least mitigate the above mentioned disadvantages.